The present invention relates to cemented carbide wear parts particularly useful in demanding wear parts applications used during sliding at high pressure and high sliding speed including seal rings with improved friction and wear properties.
Cemented carbides, particularly WCxe2x80x94Co, WCxe2x80x94TiCxe2x80x94Co, WCxe2x80x94TaCxe2x80x94Co, WCxe2x80x94TiCxe2x80x94TaCxe2x80x94Co materials, find many applications in the field of wear parts. This is linked to their outstanding mechanical properties, e.g. a unique combination of hardness and toughness resulting in high wear resistance, low friction and high thermal conductivity.
Cemented carbides with a very fine grain size, often referred to as nanocrystalline structure, i.e. with carbide grains in the order of nanometers in size, show better mechanical properties than conventional, coarse grained materials. Although nanocrystalline cemented carbides have been manufactured, problems in their production make them expensive.
There are however several examples of applications where nanocrystalline materials are very interesting candidates, such as metal cutting inserts, wood cutting teeth, etc.
An industrially important example is cemented carbides used in seal rings for pumps working under heavy-duty conditions, such as drainage pumps and seawater pumps. The seal ring package, as shown for example, FIG. 1, is often left on the shelf for a prolonged prior of time before use, resulting in a joining OR or sticking together of the seal rings caused by the surrounding air, which causes severe seal/pump damage during the starting up moment as a result. Also the running-in period of the seal ring package or the bearing package could give problems in applications with high demands on the friction and wear properties. An early fracture of the cemented carbide in the seal surface can totally destroy the seal surface. In some applications it is therefore necessary to use a combination of two types of materials in the seal rings, e.g. hard sintered SiC against cemented carbide. Such material combinations put high demands on the surface hardness and the friction properties of the softer cemented carbide.
An interesting alternative to the manufacture of entirely nanocrystalline parts would be the creation of nanocrystalline surface layers on parts with a bulk of conventional coarse grained cemented carbides.
In acidic environments the corrosion resistance of Co is low. By replacing Co with another more corrosion resistant metal, e.g. Cr, Ni or Mo or combinations thereof, the corrosion resistance of the material is increased. An alternative to the manufacture of parts with the entire material based on corrosion resistant metal would be the creation of a surface layer consisting of WC and a corrosion resistant metal mixed with Co.
In a first aspect, the present invention provides a cemented carbide wear part with a wear surface based on WC and a binder phase of Co, Ni and/or Fe, wherein said wear surface comprises a surface layer with a thickness of 0.5 xcexcm to 25 xcexcm and an average grain size less than 500 nm.
In a second aspect, the present invention provides a method of making a cemented carbide wear part with a wear surface, the method comprising: lapping the wear surface with an abrasive disc for at least 10 minutes at 1000 to 3000 rpm with an abrasive disc at a pressure of 0.1 to 0.5 MPa